Hand Wheel Position Detection System

ABSTRACT

A steering system for detecting a hand wheel position is provided and includes an input shaft connected to a hand wheel, a main gear disposed around the input shaft, a puck gear meshingly engaged with the main gear, and a control module. The control module receives an angular main position of the main gear and an angular puck position of the puck gear. The control module includes a rotational calculation module for calculating the hand wheel position based on at least the angular main position and the angular puck position.

CROSS-REFERENCES TO RELATED APPLICATIONS

This patent application claims priority to U.S. Provisional PatentApplication Ser. No. 61/579,770 filed Dec. 23, 2011 which is herebyincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a steering system, and moreparticularly to a steering system for detecting a hand wheel position.

Some types of steering systems may require the detection of hand wheelposition to provide safety features, or for certain types of algorithms.Several approaches currently exist for determining the hand wheelposition. However, some of these approaches may not include the level ofprecision that is needed. For example, one type of hand wheel positiondetection system may require a five degree diagnostic limit Hand wheelposition detection systems that are currently available may not be ableto meet this requirement.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a steering system fordetecting a hand wheel position is provided. The steering systemincludes an input shaft connected to a hand wheel, a main gear disposedaround the input shaft, a puck gear meshingly engaged with the maingear, and a control module. The control module receives an angular mainposition of the main gear and an angular puck position of the puck gear.The control module includes a rotational calculation module forcalculating the hand wheel position based on at least the angular mainposition and the angular puck position.

According to another aspect of the invention, a steering system fordetecting a hand wheel position is provided. The steering systemincludes an input shaft connected to a hand wheel, a main gear disposedaround the input shaft, a puck gear meshingly engaged with the maingear, and a control module. The control module receives an angular mainposition of the main gear and an angular puck position of the puck gear.The control module includes a rotational calculation module forcalculating the hand wheel position based on at least the angular mainposition and the angular puck position. The control module includes adiagnostic module for determining an error of the hand wheel position bycomparing the hand wheel position with a second hand wheel position.

These and other advantages and features will become more apparent fromthe following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is an exemplary steering system for detecting a hand wheelposition according to one aspect of the invention;

FIG. 2 is a dataflow diagram illustrating a control module shown in FIG.1, according to another aspect of the invention;

FIG. 3 is a graph illustrating an output of a first magnetic sensor anda second magnetic sensor shown in FIG. 1, according to yet anotheraspect of the invention;

FIG. 4 is another graph illustrating an output of a first magneticsensor and a second magnetic sensor shown in FIG. 1, according to yetanother aspect of the invention;

FIG. 5 is yet another graph illustrating an output of a first magneticsensor and a second magnetic sensor shown in FIG. 1, according to yetanother aspect of the invention; and

FIG. 6 is another graph illustrating yet another output of a firstmagnetic sensor and a second magnetic sensor shown in FIG. 1, accordingto yet another aspect of the invention.

DETAILED DESCRIPTION

Referring now to FIG. 1, where the invention will be described withreference to specific embodiments without limiting same, an exemplaryembodiment of a steering system 10 is illustrated. The steering system10 includes a hand wheel 20, an input shaft 22, a main gear 24, a ringmagnet 26, a puck gear 30, and an output shaft 34. A distal end 38 ofthe input shaft 22 attaches to the hand wheel 20. The input shaft 22 andthe output shaft 34 both extend along a longitudinal axis A-A. Thesteering system 10 is configured for detecting an angular position ofthe hand wheel 20 as the hand wheel 20 is rotated about the longitudinalaxis A-A by an operator. In one embodiment, the hand wheel 20 may berotated by an operator to manipulate a vehicle (not shown), however itis understood that the steering system 10 may be used in a variety ofapproaches.

The ring magnet 26 is disposed around the input shaft 22 and is locatedwithin the main gear 24. The puck gear 30 includes a puck magnet (notshown) that is molded into the puck gear 30. In the exemplary embodimentas shown in FIG. 1, the main gear 24 and the puck gear 30 are spurgears. A plurality of teeth 40 of the main gear 24 are meshingly engagedwith the plurality of teeth 42 of the puck gear 30. As the input shaft22 is rotated about the longitudinal axis A-A by the hand wheel 20, themain gear 24 rotates about the longitudinal axis A-A as well. The maingear 24 drives the puck gear 30, where the puck gear 30 rotates about asecondary axis B-B that is offset from the longitudinal axis A-A. In oneembodiment, the main gear 24 and the puck gear 30 have a gear ratio ofabout 1:2.2.

A plurality of first magnetic field sensors 50 are provided fordetecting the position of the ring magnet 26 located within the maingear 24, and plurality of second magnetic field sensors 52 are providedfor detecting the position of the puck gear 30 (the second magneticfield sensor 52 is shown in phantom line). The first and second magneticfield sensors 50 and 52 may be any type of sensor for detecting theangular position of the ring magnet 36 or the puck gear 30 such as, forexample, a Hall effect sensor. A control module 60 is in communicationwith the first magnetic field sensors 50 and the second magnetic fieldsensors 52 through an interface 58.

The control module 60 controls the operation of the power steeringsystem 10. Referring now to FIG. 2, a dataflow diagram illustrates anexemplary embodiment of the control module 60 of FIG. 1 used to controlthe steering system 10 of FIG. 1. In various embodiments, the controlmodule 60 may include one or more sub-modules and datastores. As usedherein the terms module and sub-module refer to an application specificintegrated circuit (ASIC), an electronic circuit, a processor (shared,dedicated, or group) and memory that executes one or more software orfirmware programs, a combinational logic circuit, and/or other suitablecomponents that provide the described functionality. As can beappreciated, the sub-modules shown in FIG. 2 can be combined and/orfurther partitioned to similarly determine the angular position of thehand wheel 20.

FIG. 3 is a graph illustrating the output of the first and secondmagnetic field sensors 50 and 52 as the hand wheel 20 (shown in FIG. 1)is rotated about the longitudinal axis A-A. Specifically, FIG. 3illustrates five revolutions of the hand wheel 20 (which is a rotationof about 1799 degrees). FIG. 3 also shows the respective angularpositions of the ring magnet 26 (shown in FIG. 1) denoted as Line A andthe puck gear 30 denoted as Line B, which range from about 0 to about360 degrees. Referring now to both FIGS. 1-3, the control module 60receives as inputs the angular position from the ring magnet 26 (shownin FIG. 1), which is denoted as c₁, as well as the angular position fromthe puck gear 30 (shown in FIG. 1), which is denoted as c₂.

FIG. 2 illustrates the control module 60 including a rotationalcalculation module 62, a lookup table 64, a diagnostic module 66, and anoffset module 70. The rotational calculation module 62 receives asinputs the ring magnet angle c₁ and the puck gear angle c₂. A hand wheelposition α is related to the ring magnet angle c₁ and the puck gearangle c₂ by equations 1-3:

c ₁=α−360 n ₁  (Equation 1)

c ₂ =Gα−360 n ₂  (Equation 2)

α=c ₁+360 n ₁  (Equation 3)

where n₁ is the number of rotations of the input shaft 22 (having atotal of 5 rotations, within the range of 0 to 1799 degrees) and n₂ isthe number of rotations of the puck gear 30 (having a total of 11rotations). Using equations 1-2 above, equation 4 may be derived as:

1/360[c ₁−1/G c ₂]=1/G n ₂ −n ₁  (Equation 4)

where G is the gear ratio. For a given value of n₁ and n₂, there is aunique value for [c₁−1/G c₂]. The term [c₁−1/G c₂] is an empirical valuethat is used to determine the number of rotations of the input shaft n₁.In one approach, a gear ratio of 1:2.2 may be used (e.g., thus equation4 would be 1/360[c₁−1/2.2 c₂]=1/2.2 n₂−n₁). Turning now to FIG. 4, basedon equation 4, the term [c₁−1/G c₂] is plotted as a dashed line, and isreferred to as Line C. Based on Line C shown in FIG. 4, the followingTable 1 may be generated in a memory of the control module 60, and issaved as the lookup table 64 (shown in FIG. 2):

TABLE 1 Line C Level n₁ n₂ 0 0 0 163 0 1 327 0 2 −33 1 2 130 1 3 294 1 4−66 2 4 98 2 5 261 2 6 −99 3 6 65 3 7 229 3 8 −131 4 8 32 4 9 196 4 10

Referring now to Table 1 and FIGS. 2-4, the rotational calculationmodule 62 determines the value for the term [c₁−1/G c₂] using Line C inFIG. 4. It should be noted that because the values for Line C aresubstantially different from one another (i.e. each of the values forLine C have a difference of at least about thirty degrees from oneanother), the values are tolerable to noise. The rotational calculationmodule 62 then finds the value for the number of rotations of the inputshaft n₁ using Table 1. The rotational calculation module 62 thencalculates the value of the hand wheel position α using equation 3. Forexample, if the inputs into the rotational calculation module 62 are 290for the ring magnet angle c₁ and 350 for the puck gear angle c₂, thenthe term [c₁−1/G c₂] yields 130. Referring to Table 1, if Line C (shownin FIG. 4) has a value of 130, then n₁ is 1. Therefore, using equation3, the hand wheel position α will be 650 degrees.

Referring to FIGS. 1 and 3-4, the respective positions of the ringmagnet 26 (Line A) and the puck gear 30 (Line B) should be generallyaligned at zero degrees (at the hand wheel position) to accuratelycalculate the hand wheel position α. However, referring now to FIG. 5,sometimes the positions of the ring magnet 26 (Line A) and the puck gear30 (Line B) are not aligned at zero degrees. For example, FIG. 5illustrates Line A with an offset of 150 degrees and Line B with anoffset of 100 degrees. In this example, the offset module 70 includes analignment algorithm for adjusting the values of the ring magnet angle c₁and the puck gear angle c₂. The alignment algorithm results in adjustedvalues for Line A and Line B, and are denoted as Line A′ and Line B′(shown in phantom line). In one embodiment, the offset module 70 (shownin FIG. 2) calculates values for a new ring magnet angle new_c₁ usingthe following algorithm:

If (c ₁ −c ₁ _(—) _(offset))<0

new_(—) c1=(c ₁ −c ₁ _(—) _(offset))+360

Else if (c ₁ −c ₁ _(—offset) )>360

new_(—) c ₁=(c ₁ −c ₁ _(—offset) )−360

Else

new_c₁=c₁

where c₁ is the position of the ring magnet 26 indicated by Line A′, andc₁ _(—) new is 150 degrees. A similar algorithm may be provided tocalculate a new puck gear angle new_c₂ as well.

Referring to FIGS. 1-4, during operation of the steering assembly 10,issues such as, for example, a sudden glitch in one of the signals forthe ring magnet angle c₁ or the puck gear angle c₂, noise in the signalsfor the ring magnet angle c₁ or the puck gear angle c₂, gear slippagebetween the ring magnet 26 and the puck gear 30, breakage of either theteeth 40 of the main gear 24 or the teeth 42 of the puck gear 30, gearlash, or the ring magnet 26 falling off the main gear 24 may occur.These issues may be detected by a diagnostic algorithm that iscalculated by the diagnostic module 66 shown in FIG. 2. The diagnosticmodule 66 calculates separate values for the hand wheel position α basedon the ring magnet angle cl and the puck gear angle c2, respectively.Specifically, the diagnostic module 66 receives as inputs the ringmagnet angle c₁ and the puck gear angle c₂, as well as the number ofrotations of the input shaft n₁ and the number of rotations of the puckgear n₂. The diagnostic module 66 calculates the hand wheel position αusing equation 3, and a second hand wheel position α′ using equation 5:

α′=(c ₂+360 n ₂)/G  (Equation 5)

The diagnostic module 66 then determines the error within the hand wheelposition α by comparing the hand wheel position α using equation 3, anda second hand wheel position α′, and determining if the differencebetween the two values is above a threshold value. The error may becalculated by equation 6:

|α−α′|=Error  (Equation 6)

The error in equation 6 may be set to any threshold value. In oneexemplary embodiment, the error may be set to a threshold value of fivedegrees. Thus, if the term |α−α′| results in more than five degrees,this indicates the error has exceeded the threshold value.

Turning now to FIG. 6, gear lashing between the main gear 24 and thepuck gear 30 may occur, which may result in rollover values near a LockPosition A (located at about zero degrees) and a Lock Position B(located at about 1799 degrees). Thus, Line C may include additionalvalues, where a Level A value and a Level B value is included. In theexemplary embodiment as shown, the Level A value is about −163 degreesand the Level B value is about 359 degrees.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description.

Having thus described the invention, it is claimed:
 1. A steering systemfor detecting a hand wheel position, comprising: an input shaftconnected to a hand wheel; a main gear disposed around the input shaft;a puck gear meshingly engaged with the main gear; and a control modulethat receives an angular main position of the main gear and an angularpuck position of the puck gear, the control module including: arotational calculation module for calculating the hand wheel positionbased on at least the angular main position and the angular puckposition.
 2. The steering system as recited in claim 1, wherein the handwheel position is calculated by: c₁=α−360 n₁, c₂=Gα−360 n₂, and α=c₁+360n₁, wherein c₁ is the angular main position, c₂ is the angular puckposition, α is the hand wheel position, n₁ is a number of rotations ofthe input shaft, n₂ is a number of rotations of the puck gear, and G isa gear ratio.
 3. The steering system as recited in claim 2, wherein aterm [c₁−1/G c₂] is an empirical value used to determine a number ofrotations of the input shaft and is compared to a value in a lookuptable saved in a memory of the control module.
 4. The steering system asrecited in claim 3, wherein the term [c₁−1/G c₂] differs by at leastthirty degrees depending on the angular main position c₁, the angularpuck position c₁, the hand wheel position α, the number of rotations ofthe input shaft n₁, and the number of rotations of the puck gear n₂. 5.The steering system as recited in claim 1, wherein a position of themain gear and a position of the puck gear are aligned generally at zerodegrees.
 6. The steering system as recited in claim 1, wherein aposition of the main gear and a position of the puck gear are offsetfrom zero degrees.
 7. The steering system as recited in claim 6, whereinthe control module includes an offset module, and wherein the offsetmodule executes an alignment algorithm for adjusting the position of themain gear and the position of the puck gear.
 8. The steering system asrecited in claim 1, wherein the control module includes a diagnosticmodule that receives the angular main position, the angular puckposition, a number of rotations of the input shaft, and a number ofrotations of the puck gear.
 9. The steering system as recited in claim8, wherein the diagnostic module calculates the hand wheel position anda second hand wheel position.
 10. The steering system as recited inclaim 9, wherein the second hand wheel position is calculated by:α′=(c ₂+360 n₂)/G wherein α′ is the second hand wheel position, c₂ isthe angular puck position of the puck gear, n₂ is a number of rotationsof the puck gear, and G is a gear ratio.
 11. The steering system asrecited in claim 9, wherein the diagnostic module determines an error ofthe hand wheel position by comparing the hand wheel position with thesecond hand wheel position.
 12. The steering system as recited in claim11, wherein the diagnostic module determines if the error is above athreshold value.
 13. A steering system for detecting a hand wheelposition, comprising: an input shaft connected to a hand wheel; a maingear disposed around the input shaft; a puck gear meshingly engaged withthe main gear; and a control module that receives an angular mainposition of the main gear and an angular puck position of the puck gear,the control module including: a rotational calculation module forcalculating the hand wheel position based on at least the angular mainposition and the angular puck position; and a diagnostic module fordetermining an error of the hand wheel position by comparing the handwheel position with a second hand wheel position.
 14. The steeringsystem as recited in claim 13, wherein the hand wheel position iscalculated by: c₁=α−360 n₁, c₂=Gα−360 n₂, and α=c₁+360 n₁, wherein c₁ isthe angular main position, c₂ is the angular puck position, α is thehand wheel position, n₁ is a number of rotations of the input shaft, n₂is a number of rotations of the puck gear, and G is a gear ratio. 15.The steering system as recited in claim 14, wherein a term [c₁−1/G c₂]is an empirical value used to determine a number of rotations of theinput shaft and is compared to a value in a lookup table saved in amemory of the control module.
 16. The steering system as recited inclaim 15, wherein the term [c₁−1/G c₂] differs by at least thirtydegrees depending on the angular main position c₁, the angular puckposition c₁, the hand wheel position α, the number of rotations of theinput shaft n₁, and the number of rotations of the puck gear n₂.
 17. Thesteering system as recited in claim 13, wherein a position of the maingear and a position of the puck gear are aligned generally at zerodegrees.
 18. The steering system as recited in claim 13, wherein aposition of the main gear and a position of the puck gear are offsetfrom zero degrees.
 19. The steering system as recited in claim 18,wherein the control module includes an offset module, and wherein theoffset module executes an alignment algorithm for adjusting the positionof the main gear and the position of the puck gear.
 20. The steeringsystem as recited in claim 1, wherein the diagnostic module receives theangular main position, the angular puck position, a number of rotationsof the input shaft, and a number of rotations of the puck gear, andwherein the second hand wheel position is calculated by:α′=(c ₂+360 n ₂)/G wherein α′ is the second hand wheel position, c₂ isthe angular puck position of the puck gear, n₂ is a number of rotationsof the puck gear, and G is a gear ratio.